At the Mother of Mercy Hospital, deep in rebel-held territory in southern Sudan’s Nuba Mountains, 14-year-old Daniel Omar describes how, on a bright clear day in early March, a bomb dropped by his own government blew off both his hands. “I was at El Dar, taking care of our cows,” he says. “I heard the sound of an Antonov so I lay down. Then I could hear that it had released a bomb and it was coming down on me. So I jumped up, ran behind a tree, and wrapped my arms around it.” The bomb landed a few yards away. The tree, a hardy desert thorn with a thick trunk, protected Daniel’s body but his hands were exposed to the blast. The explosion ripped them clean off. “I saw blood,” says Daniel. “I saw my hands were not there. I could not even cry. I stood up, and started walking, then I fell down. A soldier came and picked me up and put me in the shade. Then he got a car. And they washed and bandaged me, and brought me here.”

There’s generally little truth to those stories of Africa — a continent of more than 50 countries and a billion people — which contrive to lionize Westerners. But in the case of Daniel and hundreds of others, the only reason they are alive to tell their stories is because of the attentions of a single American surgeon, Dr. Tom Catena, who has lived in the Nuba Mountains since 2008.

Catena, 47, from upstate New York, had already been working in the Nuba Mountains for three years when the government of Sudan in Khartoum launched an attack on the Nuba rebels last June. What began as an assault on the guerrillas quickly became an all-out ethnic assault on the general population. In government-held areas, civilians were likely executed en masse: the Satellite Sentinel Project, which monitors atrocities and troop movements in Sudan from the air, says it has found what look like a total of eight mass graves in and around the regional capital of Kadugli.

The only surgeon at the only hospital in the Nuba capable of dealing with severe war injuries is Catena. As such, there is perhaps no one better qualified to describe what Khartoum is doing to its own citizens. I ask Catena how many war wounded he has treated since the fighting started: 822, he says. Of those 140 required minor surgery and 102 major surgery, mostly amputations. Catena adds a total of 73 of his most seriously wounded patients were injured by Antonov bombings. He is unequivocal about Khartoum’s intentions. It is, he says, “premeditated civilian bombing … to terrorize people and force them out of their homes, and their land.”

Catholic Medical Mission Board

This is the second time I’ve met Catena. The first was last June as Khartoum’s campaign of ethnic cleansing began. Then he allowed me to wander his hospital wards, collecting testimonies. Ten months later, he looks gaunt. Continually on call, Catena hasn’t left the hospital compound in 14 months, despite the ever-present threat of an attack. “I don’t know why we haven’t been bombed,” he says. “Every time they fly over, I think: ‘Is this the day?’ It’s not like these guys would have any morals or qualms about it. They’ve bombed hospitals before.” Explaining his wan appearance, he says he has “a touch of malaria.” He has also been affected, he says, by the death the night before of a patient. “He had 20 holes in his intestines,” says Catena. “We fixed them and he recovered – every night we were doing something for him, but he’d turned around and was doing great, just cruising. Then basically he upped and died at three in the morning. I can’t explain it.”

Catena is very clear about what drew him to the Nuba Mountains, however: his Christian faith. He had always intended to work as a missionary and, after initially qualifying as a mechanical engineer, he returned to school to study medicine when “I realized mechanical engineering doesn’t much lend itself to missionary work.” Once he paid his debt to the Navy for paying his way through medical school, serving as a medic to Navy pilots, he began work in Africa, first in Kenya, then South Sudan, then at Mother of Mercy, where he has been since it opened in March 2008. “The idea is to serve,” he says. “You use Christ as your guide, your mentor. This is what he did. He came to serve, not be served, and I try to follow that.”

Catena’s faith also persuaded him to stay after the outbreak of war, even when his overseers wanted him to pull out. “What the heck?” he exclaims. “We’re supposed to be missionaries. The time of Christ is when you are supposed to stick around. It’s not a time to bail.” He is no proselytizer, however. It wouldn’t work with the Nuba, who – in contrast to the belligerent, chauvinist Islam of their government in Khartoum – freely mix religions, even within a family. Daniel is a case in point. Wearing a cross around his neck, he says: “My father and mother are Muslims. But from the moment I started talking, I decided I was a Christian. They let me.”

Catena’s faith also doesn’t inhibit him from imagining some earthly, pragmatic solutions to the suffering he sees every day. “We need to open up a humanitarian corridor,” he says. “A no-fly zone is a good idea but the argument is that it’s too expensive. Well, I was with a Navy f-18 squadron and I know a single squadron could finish off the entire Sudanese air force in a day.” Catena’s anger is stoked further by the thought that soon he might be treating a second wave of victims of the civilian bombardments. Most families have fled their villages, some for refugee camps in South Sudan, but hundreds of thousands more have sought refuge in the caves that dot the red-boulder Nuba Mountains. Displaced and unable to farm, a hunger crisis – and perhaps an ethnic exodus – looms.

Ultimately, even for a surgeon who is, by now, most likely one of the world’s most experienced amputators, there are things he can’t fix. After a little more than a month, Daniel’s arms have healed into neat, smooth stumps, with barely a scar. The same can’t be said of his mind. “Without hands, I can’t do anything,” says Daniel. “I can’t even fight. I’m going to make such hard work for my family in the future.” He looks me straight in the eye. “If I could have died, I would have,” he says.